Light emitting diode module

ABSTRACT

A light emitting diode module having improved luminous efficiency is provided. The light emitting diode module includes: a light emitting chip; a phosphor layer formed of phosphor materials emitting light having a wavelength longer than the light emitted from the light emitting chip using light emitted from the light emitting chip as an excitation source; and a reflection plate that is disposed between the light emitting chip and the phosphor layer and that reflects the light emitted by the phosphor layer.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a divisional of U.S. application Ser. No.11/513,221, filed Aug. 31, 2006, and claims the benefit of Korean PatentApplication No. 10-2006-0010179, filed on Feb. 2, 2006 in the KoreanIntellectual Property Office, the entire contents of which isincorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to a light emitting diode module, andmore particularly, to a light emitting diode module with an improvedstructure providing an improved luminous efficiency for realizing whitelight or colored light while using a light emitting diode emitting blueor ultraviolet light and phosphor materials.

2. Description of the Related Art

A light emitting diode (LED) is formed of a light emitting source usingcompound semiconductors, such as GaAS, AlGaN, and AlGaAs, to generatevarious colors of light. LEDs can be easily manufactured and controlledcompared to semiconductor lasers and have longer life spans thanfluorescent lamps, and thus have replaced fluorescent lamps as theillumination light sources for next generation display devices.Recently, blue light emitting diodes and ultraviolet light emittingdiodes which are produced using nitride materials and having excellentphysical and chemical characteristics, have been introduced. Inaddition, as white light and other colors can be produced using blue orultraviolet light emitting diodes together with phosphor materials, theapplication range of light emitting diodes has been enlarged.

LED modules using phosphor materials produce white light or other colorsof light according to the principle that light emitted from the blue orultraviolet light emitting diode and incident on the phosphor materialtransmits energy to the phosphor material, and thus light with a longerwavelength than incident light is emitted. For example, in a white lightemitting diode module, photons of ultraviolet light emitted from the LEDchip excite the phosphor material and thus a combination of red, green,and blue light or a combination of yellow and blue light is emitted fromthe excited phosphor material. The wavelengths of the visible lightemitted from the phosphor material vary according to the composition ofthe phosphor material, and this combination of visible light appears aswhite light to human eyes.

FIG. 1 is a schematic view of a conventional LED module. Referring toFIG. 1, in the LED module, a light emitting chip 1 is disposed in aconcave recess on a base 6, a first resin layer 3 is coated inside thebase 6, and a second resin layer 4 and a third resin layer 5 are coatedsequentially on top of the first resin layer 3.

However, in the configuration described above, the light extractionefficiency is low. Light extraction efficiency refers to the ratio ofthe amount of the light generated in the light emitting chips 1 to theamount of the light actually emitted from the LED module, and isdirectly related to the luminous efficiency, which denotes theilluminating performance of the LED module.

FIG. 2 illustrates the path of the light emitted by excited phosphorlayers in the structure of the LED module of FIG. 1. Referring to FIG.2, the light is emitted by the excited phosphor materials over 360°.Accordingly, light that is not fully emitted outward and is insteademitted in the downward direction of FIG. 2 is thus counted as lossresulting in a decrease in the luminous efficiency of the LED module.

SUMMARY OF THE DISCLOSURE

The present invention may provide a light emitting diode (LED) modulewith a structure having high luminous efficiency.

According to an aspect of the present invention, there may be provided alight emitting diode module comprising: a light emitting chip; aphosphor layer formed of phosphor materials emitting light having alonger wavelength than the light emitted from the light emitting chipusing light emitted from the light emitting chip as an excitationsource; and a reflection plate that is disposed between the lightemitting chip and the phosphor layer, and that reflects the lightemitted from the phosphor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention areillustrated in detailed exemplary embodiments thereof with reference tothe attached drawings in which:

FIG. 1 is a cross-sectional view of a conventional light emitting diode(LED) module;

FIG. 2 is a schematic view illustrating directions of light emitted froma phosphor layer in the conventional LED module of FIG. 1;

FIG. 3 is a cross-sectional view of an LED module according to anembodiment of the present invention;

FIGS. 4A through 4D are perspective views illustrating reflection platesaccording to various embodiments of the present invention; and

FIG. 5 is a schematic view illustrating light that is emitted from thephosphor layer of the LED module of FIG. 3.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown.

FIG. 3 is a cross-sectional view of an LED module according to anembodiment of the present invention; and FIGS. 4A through 4D illustratea number of reflection plates according to various embodiments of thepresent invention.

Referring to FIG. 3, the LED module includes a light emitting chip 22, aphosphor layer 25 using the light emitted from the light emitting chip22 as an excitation source and emitting light of a longer wavelengththan the light emitted from the light emitting chip 22, and a reflectionplate 28 that is disposed between the phosphor layer 25 and the lightemitting chip 22 and reflects the light emitted in the downwarddirection of FIG. 3 by the excited phosphor layer 25.

The light emitting chip 22 is disposed on a submount 34 that is mountedin a dispensing member 33 having a cup-shaped inner surface 33 a. Afirst lead frame 37 and a second lead frame 40 are fixed in the lowerportion of the dispensing member 33 and protrude from the dispensingmember 33.

The first lead frame 37 and the second lead frame 40 are electricallyconnected to an n-electrode and a p-electrode of the light emitting chip22 respectively.

The light emitting chip 22 includes a p-type semiconductor layer and ann-type semiconductor layer. When power is supplied through the first andsecond lead frames 37 and 40 between the n-electrode and thep-electrode, holes of the p-type semiconductor layer and electrons ofthe n-type semiconductor layer are combined in an active layer and thuslight is generated Light is therefore emitted from the light emittingchip 22.

The wavelength of light generated in the light emitting chip 22 isdetermined according to the material and structure of the active layer,and according to the wavelength of light that is to be realized by theLED module.

The light generated and emitted by the light emitting chip 22 istransmitted through the reflection plate 28 and is incident on thephosphor layer 25 formed of a phosphor material. The incident lighttransmits energy to and excites the phosphor material, thereby changingthe color of the light. Essentially, white light or other colors ofmonochromic light can be produced by the proper combination of the lightemitting chip 22 and the phosphor layer 25 in the LED module.

For example, in one method of realizing white light, the light emittingchip 22 generates blue light, and the phosphor layer 25 is formed of ayellow phosphor material. Alternatively, the light emitting chip 22generates ultraviolet light, and the phosphor layer 25 is formed of amixture of red, green, and blue phosphor materials.

Also, the light emitting chip 22 can generate ultraviolet or blue light,and the phosphor layer 25 can be formed of a single color phosphormaterial such that an LED module emitting light of a single color havinga longer wavelength than the light generated in the light emitting chip22 can be produced.

The reflection plate 28 is disposed between the light emitting chip 22and the phosphor layer 25, and a concavo-convex pattern is formed on theupper surface of the reflection plate 28 facing the phosphor layer 25.

Referring to FIG. 4A, the concavo-convex pattern is a pattern of concaverectangular cavities. The concavo-convex pattern of FIG. 4 isillustrated as an example, and the pattern may be convex or have otherforms. For example, as illustrated in FIG. 4B, a reflection plate 29with a concavo-convex pattern of concave hemispheres can be employed.The concave-convex pattern in a preferred embodiment can be ahemispherical array or a polygonal cavity array.

The concavo-convex pattern may be formed on the upper surface of thereflection plate 28 or 29 facing the phosphor layer or on the lowersurface of the reflection plate 28 or 29 facing the light emitting chip22.

A first resin layer 43 may be formed between the light emitting chip 22and the reflection plate 28 or 29. The first resin layer 43 protects thelight emitting chip 22 and reduces the difference between the refractiveindex of the light emitting chip 22 and the refractive index of theregion into which the light is emitted from the light emitting chip 22.As the refractive index of the first resin layer 43 is similar to therefractive index of the light emitting chip 22, the amount of the lightthat is totally internally reflected at a boundary surface 22 a of thelight emitting chip 22 is decreased, thus increasing the amount of thelight that is emitted out of the light emitting chip 22.

A second resin layer 46 may be included between the reflection plate 28or 29 and the phosphor layer 25.

Some light may be internally totally reflected at a surface where aconcavo-convex pattern is not formed depending on the incidence angle,which may reduce the amount of light emitted from the LED module andthus reduce the luminous efficiency. Accordingly, when a concavo-convexpattern is formed only on the upper surface of the reflection plate 28or 29 facing the phosphor layer 25 and the lower surface of thereflection plate 28 or 29 facing the light emitting chip 22 is flat, therefractive index of the first resin layer 43 may preferably be smallerthan the refractive index of the reflection plate 28 or 29.

Also, when a concavo-convex pattern is formed only on the lower surfaceof the reflection plate 28 or 29 facing the light emitting chip 22 andthe surface of the reflection plate 28 or 29 facing the phosphor layer25 is flat, the refractive index of the second resin layer 46 maypreferably be greater than the refractive index of the reflection plate28 or 29.

Referring to FIG. 4C, a reflection plate 30 may have a flat uppersurface facing the phosphor layer 25 and a flat lower surface facing thelight emitting chip 22. In this case, the refractive index of the firstresin layer 43 may be smaller than the refractive index of thereflection plate 30, and the refractive index of the second resin layer46 may be greater than the refractive index of the reflection plate 30in order to reduce the loss of the light emitted from the light emittingchip 22 due to total internal reflection of some of the light at twoboundary surfaces of the reflection plate 30. Also, this relativelyhigher refractive index of the second resin layer 46 is preferable inconsideration of the light emitted from the excited phosphor layer 25since the amount of the light that is reflected back towards thephosphor layer 25 by the reflection plate 30 increases.

Referring to FIG. 4D, a reflection plate 31 may be formed of multiplelayers of different materials having different refractive indices. Inthis instance, the refractive index of the layer that is disposed closerto the phosphor layer 25 may preferably be greater. Thus, as describedabove, for the light emitted from the light emitting chip 22 andtransmitted through the reflection plate 31 and through the phosphorlayer and emitted from the LED module, the loss due to the totalinternal reflection is minimized and for the light emitted from thephosphor layer 25, the amount of light that is reflected back toward thephosphor layer 25 is increased.

FIG. 5 is a schematic view illustrating the light emitted from the lightemitting chip 22 and the light emitted from the excited phosphor layer25. Referring to FIG. 5, the light emitted from the light emitting chip22 is transmitted through the reflection plate 28 and is incident on thephosphor layer 25.

The light incident on the phosphor layer 25 transmits energy to thephosphor materials, and consequently light having a longer wavelengththan the incident light is emitted. The light is emitted in alldirections above and below the phosphor layer 25. The reflection plate28, disposed between the phosphor layer 25 and the light emitting chip22, reflects the light which is not emitted from the LED module by thephosphor layer 25 but which is incident on the reflection plate 28 backtowards the phosphor layer 25, thereby increasing the luminousefficiency.

Also, the concavo-convex pattern formed on the reflection plate 28effectively diverges the light emitted by the phosphor layer 25 so as toemit the light from the LED module, which is preferred. The materialforming the reflection plate 28, or the size and arrangement periods ofthe cavities of the concavo-convex pattern may be determined accordingto the wavelength of the light emitted from the light emitting chip 22and the wavelength of the light emitted from the phosphor layer 25 orother related properties.

Examples of materials which can form the reflection plates 28 through 31are SiO₂, Al₂O₃, AlN, and ZnSe.

Table 1 shows a comparison between the illumination efficiency of an LEDmodule according to an embodiment of the present invention and theillumination efficiency of a conventional LED module.

TABLE 1 Brightness Illumination Current (A) Power (W) (lm) Efficiency(lm/W) Present 0.35 0.151 32.96 26.6 Embodiment Comparative 0.35 0.09727.99 22.7 Example

The LED modules used to obtain these results included a light emittingchip emitting light of a wavelength of around 400 nm and a phosphorlayer formed of a mixture of red, green, and blue phosphor materials.The first and second resin layers were formed of silicon resin, and theconcavo-convex pattern of the reflection plate was the same as thepattern of FIG. 4B. The light emitted from the light emitting chip wasincident on the phosphor layer and excited the phosphors to emit red,blue, and green light, which were used to realize white light.

Luminous efficiency is used as an index denoting the illuminatingperformance of the LED module, which refers to the brightness sensed bya human eye per watt of supplied power, the brightness being measured inunits of lumens (lm). The luminous efficiency of the LED moduleaccording to the present embodiment was 26.6 lm/W and the luminousefficiency of the conventional LED module was 22.7 lm/W. Thus the LEDmodule according to the present embodiment had a luminous efficiencythat was 17% higher than the luminous efficiency of the conventional LEDmodule.

In the LED module described above according to the present invention, areflection plate reflecting the light emitted from the phosphor layerbetween the phosphor layer and the light emitting chip is used toimprove the luminous efficiency of an LED module for realizing whitelight or single color light using a light emitting chip and a phosphorlayer. Also, a fine concavo-convex pattern is formed on at least onesurface of the reflection plate to increase the luminous efficiency.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A light emitting diode module comprising: a light emitting chip; aphosphor layer formed of phosphor materials emitting light having alonger wavelength than the light emitted from the light emitting chipusing light emitted from the light emitting chip as an excitationsource; and a reflection plate that is disposed between the lightemitting chip and the phosphor layer, and that reflects light emittedfrom the phosphor layer, wherein a concavo-convex pattern is formed onthe surface of the reflection plate which faces the light emitting chip.2. The light emitting diode module of 1, wherein the concavo-convexpattern is a hemispherical array or a polygonal cavity array.
 3. Thelight emitting diode module of claim 1, further comprising a resin layerthat has a refractive index greater than the refractive index of thereflection plate and is formed between the reflection plate and thephosphor layer.
 4. The light emitting diode module of claim 1, whereinthe reflection plate is formed of a material selected from the groupconsisting of SiO₂, Al₂O₃, AlN, and ZnSe.